1. Field of the Invention
The present invention relates generally to shaped plant growth nutrient products and to processes for producing such shaped plant growth products. More particularly, it relates to products prepared by mixing active plant growth ingredients such as coated and uncoated plant nutrients with a biodegradable, water dispersible, water soluble, thermoplastic polymeric binding agent to produce shaped plant growth nutrient products such as fertilizer products, preferably in tablet form. The invention further relates to processes for producing such shaped plant growth nutrient products as well as to methods for using such shaped products for treating plants and vegetation.
2. Description of Related Art
Shaped plant nutrient formulations in tablet, spike or other forms have been known heretofore for targeting the application of plant growth nutrients to plants in a defined area. Exemplary of such prior products are those described in published European Patent Application EP0380193 A2. That published application describes the preparation and application of molded bodies containing nutrients, active ingredients, plant treatment agents and auxiliaries. The molded bodies are made from particles bound together by substance bridges consisting of thermally or chemically hardened binding agents including epoxy resins and polyurethane resins. It should be noted that both polyurethane and the epoxy resins are crosslinked resins and, therefore, are insoluble in water or other solvents.
U.S. Pat. No. 4,055,974 describes fertilizer tablets prepared from particles of fertilizer source materials which are bonded together with water insoluble, water swellable, hydrophilic polymeric gels by a cured water insoluble thermoset resinous binder such as urea formaldehyde. The resulting tablets are described as being adapted to absorb water and disintegrate. However, as with the tablets described in European Patent Application EP0380193 A2, the water insoluble binders cause undesirable environmental results due to their slow degradation properties when applied to the plant soil.
Furthermore, since the binder employed to produce the tablets in accordance with U.S. Pat. No. 4,055,974 is a thermoset resin, efficient and cost effective melt processing techniques to produce the tablets cannot be performed and the cost and efficiency in producing the tablets is adversely impacted.
U.S. Pat. No. 4,011,061 describes the production of fertilizer tablets employing organic, film-forming preferably thermoplastic resin binders which are water insoluble and present environmental problems while U.S. Pat. No. 4,752,317 describes the production of a highly compacted product sold as a spike or a tablet. The product is prepared by mixing fertilizer ingredients with a water dispersible hydrolyzed lignosulfonate-acrylonitrile graft copolymer binder which is water soluble but not thermoplastic and presents problems relating to the techniques required to produce the product.
Several commercial products are presently on the market which comprise tablets prepared from fertilizer granules and polyurethane binders. However, these tablets all exhibit environmental disadvantages attributable to the durability of the polyurethane binder systems employed. For example, when so-called controlled release fertilizer (CRF) granules in such a tablet fully release their nutrients to a treated plant, the tablet retains its initial shape as if the fertilizer tablet has not been active. Furthermore, the production of these prior plant growth nutrient tablets has resulted in various problems such as those encountered concerning the build-up of cured resin residue on the tablet forming mold which is difficult to remove.
Another example of current products being marketed is presented by tablets prepared from coated fertilizer granules and a water swellable, thermosetting polymeric binder system. However, as a result of its inability to melt, in production the polymeric binder must be applied from the constituent monomers or prepolymers in an emulsion or solution, which requires an additional drying stage in the tablet production process. The ultimate thermoset resin is formed upon aging.
Generally, the active plant growth/nutrient ingredients employed in the production of fertilizer tablets are coated fertilizers which, in use, have a number of advantages over uncoated fertilizers and are known to be very effective sources to provide controlled release of nutrients for the feeding of plants. The nutrients are released through the fertilizer's coating at controlled rates and in this way the nutritional need of the plants can be exactly matched. By selection of a suitable coating thickness or coating composition, an appropriate fertilizer longevity can be attained. By doing so, one application of these CRF's can provide the necessary nutrients for a plant that would take multiple applications of soluble fertilizer, without the risk of overfeeding of plants or leaching of fertilizer minerals to the environment.
In the CRF's, the fertilizer may release out of the coatings in various ways such as via: 1) imperfections in the coating, 2) pores in the coating or 3) osmotic pressure. It has been recognized heretofore that the latter two mechanisms offer important benefits over the first in regard to consistency of release rates.
An example of coated fertilizers which exhibit fertilizer release via coating imperfections are the sulfur coated fertilizers with a polymeric topcoat, such as disclosed in U.S. Pat. Nos. 5,219,465; 5,405,426 and 5,466,274. The major advantage of the sulfur coated fertilizers with a polymeric topcoat is their relatively low cost.
Examples of coated fertilizers which show fertilizer release through pores in the coating are presented by the polyolefin coated fertilizers such as disclosed in U.S. Pat. No. 4,019,890.
Fertilizer release by water vapor permeation through the coating and subsequent build-up of osmotic pressure is exhibited by fertilizers with solvent applied thermosetting resin coatings. Examples of solvent applied thermosetting resin coated fertilizers which are currently in use are disclosed in U.S. Pat. Nos. 3,223,518; 4,657,576; 4,880,455, 5,652,196; 5,993,505 and 6,139,597.